NLTURAL MAGNETS 



of iron rings hung one from another ; but from that 

 stone depends the power in all of them." (Plato's 

 Ion., Sec. 5.) 



The stone thus described is essentially one form of 

 the Black Oxide of Iron (Fe. O. Fe 2 .O 3 ), the magnetic 

 iron ore of the Iron Masters. It was early known 

 that the Lodestone could confer properties like its 

 own upon rods or strips of steel by being drawn 

 thereover frequently in one direction. After which 

 the rods would show polarity. If hung horizontally 

 so as to turn readily, the same end would always 

 point towards the North. The Chinese noticed the 

 phenomenon, and used the Magnet in navigation many 

 centuries before the Europeans invented the Mariner's 

 Compass. The property of polarization referred to 

 above is due to the fact that the globe of the earth is 

 influenced by thermo-electric currents, induced by its 

 diurnal revolution and consequent variation of temper- 

 ature, and also by other causes. These currents flow in 

 lines parallel to the Equator. A magnet when within 

 an electric field will always place itself, if at liberty 

 to move, at right angles to the direction of the flow 

 of the current, thus causing the positive pole of the 

 magnet to point towards the North in a natural ter- 

 restrial magnetic field. An electric field or current 

 such as described surrounds a magnet, and will convert 

 another piece or rod of iron into a magnet if placed 



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